Steam boiler having a water space traversed by a flue gas duct

ABSTRACT

The burner is in the form of a muffle burner in order to complete combustion before entry of the flue gas into the duct and thus create a zone of intense heat at the forward portion of the duct. Open-ended tubes are positioned in the duct transverse to the flue gas flow to conduct the water therethrough while the first few tubes have the feed water injected therethrough from a source of feed water.

United States Patent Stiefel [451 Aug. 22, 1972 STEAM BOILER HAVING A WATER SPACE TRAVERSED BY A FLUE GAS DUCT [72] Inventor: Werner Stiefel, Winterthur, Switzerland [73] Assignee: Sulzer Brothers, Ltd., Winterthur,

Switzerland 22 Filed: Sept. 16, 1970 [21] App1.No.: 72,634

[30] Foreign Appiication Priority Data Sept. 23, 1969 Switzerland..... .L.14328/69 [52] US. Cl ...122/l40 R, 122/149 431/173 511 Int. Cl ..F22b 7 04 I [58] FieldofSearch ..431/l73;'l22/140,145,146,

[56] References Cited UNITED STATES PATENTS 2,598,111 5/1952 Cuddon 122/147 659,780 10/1900 Ahem 122/145 X 1,618,808 2/1927 Burg ..431/173 2,643,645 6/1953 Kleinen 122/145 X 3,185,202 5/1965 Mitchell et a1 ..431/l73 X FOREIGN PATENTS OR APPLICATIONS 19,485 0/1899 Great Britain 122/145 Primary Examiner-Kenneth W. Sprague Attorney-Kenyon & Kenyon Reilly Carr & Chapin ABSTRACT The burner is in the form of a muffle burner in order to complete combustion before entry of the flue gas into the duct and thus create a zone of intense heat at the forward portion of the duct; Open-ended tubes are positioned in' the duct transverse to the flue gas flow to'conduct the water therethrough while the first few tubes have the feed water injected therethrough from a source of feed water.

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WERNER STIEF'EIL STEAM BOILER HAVING A WATER SPACE TRAVERSED BY A FLUE GAS DUCT This invention relates to a steam boiler in which a water space is transversed by a flue gas duct.

Steam boilers have been known in which a water space is traversed by a flue gas duct. In some of these boilers, a burner for example, an oil burner, has been disposed at the entrance to the flue gas duct so that the flue gas from the burner flows longitudinally through the flue gas duct. Since the walls of the flue gas duct have generally been formed by a corrugated tube, and since the heat transfer coeflicient from the longitudinally flowing flue gas to the tube is relatively low, these steam boilers have been relatively large.

Accordingly, it is an object of the invention to provide a steam boiler of the above type of relatively small dimension.

It is another object of the invention to increase the amount of heat transferred from a flue gas emanating from a burner to the forward part of a flue gas duct positioned at the mouth of the burner.

Briefly, the invention provides a steam boiler having a water space traversed by a flue gas duct with a muffle burner at the entrance to the flue gas duct and with a plurality of tubes mounted at least in the portion of the flue gas duct adjacent to the muffle burner which tubes are open to the water space and which are generally transverse to the direction of flow of flue gas thereby. Because the burner is a muffle burner, very hot flue gas is produced in a small space which after leaving the muffle immediately comes into contact with the tubes arranged transversely in the flue gas duct. As a result, the heat transfer to the water in the steam boiler is high. Because the tubes which are open to the water space are disposed transversely in the flue gas duct, the heat transfer coefficient both from the flue gas to these tubes and from these tubes to the water is high so that, the heat transfer surface can be housed on a small area. The boiler may therefore be compact.

In one embodiment, the flue gas duct is formed of a quadrilateral cross-section such as a rectangular crosssection while the transverse tubes are vertically arranged. In addition, the transverse tubes are formed with slightly bent upper portions above the gas duct and with oblique openings at the ends so as to cause preliminary separation of any steam bubbles passing out of the tubes.

In another embodiment, the flue gas duct is formed of rectangular cross-section and is oriented with a diagonal of the cross-section in a vertical plane. In this embodiment, the transverse tubes are disposed in a criss-cross pattern relative to the vertical diagonal of the duct and have ends of which extend upwardly in vertical planes.

In still another embodiment, the flue gas duct is formed of a rhomboid cross-section and the transverse tubes are arranged in a criss-cross pattern withends terminating slightly beyond the flue gas duct.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a vertical sectional view through a steam boiler according to the invention along a line 1-1 in FIG. 2;

FIG. 2 illustrates a cross-sectional view taken on line Il-II ofFIG. 1;

FIG. 3 illustrates a view through the flue gas duct taken on line lII-lll of FIG. 2;

FIG. 4 illustrates a modified flue gas duct according to the invention in section similar to FIG. 2; and

FIG. 5 illustrates another modified flue gas duct.

Referring to FIGS. 1 to 3, the steam boiler consists of a horizontal drum 1 which is filled with water to a level and a gas duct 2 of rectangular cross-section which traverses the water space of the drum 1. The flue gas duct 2 is defined at the top by a horizontal roof 3, at the bottom by a horizontal floor 4 and at the sides by two vertical side walls 7, 8. The side walls 7, 8 are formed of vertical finned tubes 9 which are welded to one another in a fluid-tight manner and are open at the top and bottom to the water space.

The flue gas duct 2 is connected at an inlet end (on the left as viewed in FIG. 1) to a muffle burner 30 consisting of a mufi'le 31 of ceramic material, a burner lance 32 coaxial with the muffle for liquid and/or gaseous fuel, and two annular air inlets 33, 34. The two annular air inlets 33, 34 contain swirl elements (not shown) which cause the air for combustion which is supplied in known manner (not shown) to enter the muffle 31 along a helical path, so that the flame is also subjected to a helical movement inside the muffle 31. During combustion the temperatures on the inside surface of the muffle 31 are very high so that combustion is completed inside the muffle. The flue gas duct 2 also has an outlet (on the right as viewed in FIG. 1) which leads into a deflecting chamber 40 located at one end of the drum 1.

A plurality of fire tubes 41 are mounted in parallel relation to the flue gas duct 2 and outside of the duct 2. These tubes 41 extend from the deflecting chamber 40 to a flue gas header 42 which is connected to a flue (not shown) in order to carry off the flue gas from the duct 2 into the header 42. An economizer heating surface may be provided between the header 42 and the flue.

A plurality of tubes 5 are mounted in that portion 10 of the flue gas duct 2 which is adjacent to the muffle burner 30 and are open to the water space so as to conduct a flow of water therethrough. These tubes 5 are arranged vertically in the flue gas duct 2 and are set in groups in planes perpendicular to the flue gas flow so that the flue gas can flow transversely over and past the tubes. The lower ends of the tubes 5 are welded in a fluid-tight manner to the floor 4 of the flue gas duct 2 while the upper ends 6 of the tubes 5 extend beyond the roof of the flue gas duct 2 and are bent at an angle to the vertical. The ends of these bent tube portions 6 are cut off obliquely relative to the axes of these portions 6. Where the tubes 5 pass through the roof 3 of the flue gas duct 2, the tubes 5 are welded to the roof in a fluidtight manner so that the vertical tube portions act as spacer bolts. Similarly, that portion 46 of the flue gas duct 2 which is adjacent to the deflecting chamber 40 contains similar tubes 5 which are open to the water space and on to which the flue gas flows transversely.

The boiler further includes a portion 15 within the tank 1 between the portions 10, 46 of the flue gas duct 2 which contains tubes 16 on to which the flue gas also flows transversely but which are to be traversed by steam instead of water. A box 47 is located above these tubes 16 and is fixed to the roof 3 in a fluid-tight manner while a partition 48 divides the box 47 into two chambers 17 and 18. Another box 49 is located beneath the tubes 16 and is fixed in a fluid-tight manner beneath the floor 4 of the flue gas duct 2 and forms a deflecting chamber 19 for the steam. This deflecting chamber 19 can be drained by any suitablemeans (not shown). The chamber 17 is connected by a tube 20 to the steam space above the water level 60 of the boiler, and a tube 21 from the chamber 18 leads out of the drum 1 to a point of use (not shown).

A feed-water inlet nozzle 50 for each tube 5 is pro vided below the three groups of tubes 5 nearest the muffle burner 30. The nozzles 50 are arranged on three distributors'S 1 (one for each group of tubes) which are connected to a common feed-water line 52.

In operation of the steam boiler, gas and/or oil is burnt in the muffle burner 30 and the resulting hot flue gas flowsv longitudinally through the flue gas duct 2 towards the deflecting chamber 40 while the heat of the gas is absorbed by the water flowing through the tubes '5 and by the steam flowing through the tubes 16. From the deflecting chamber 40, the flue gas passes into the fire tubes 41 and upon flowing therethrough loses more heat. to the water before leaving the boiler by way of the header 42. The feed water, which may be pre-heated in aneconomizer is fed into the boiler along the line 52 and through the nozzle 50 at a relatively high exit speed so that water is also forced out of the water space into the tubes 5 in the first three groups. This ensures that these groups of tubes, which are subject to the more intense heat from the flue gas are cooled. The water then flows through the other groups of tubes 5 by convection. The quantity of working medium flowing through these tubes is increased by the tube portions 6 which act like flues. The bending of the tube portions 6 both provide a space for the fire tubes 41 and causes preliminary separation of the steam bubbles which form during operation so that the water flowing downwards on the right as viewed in Fig. 2 is practically free of steam bubbles. The steam collecting in the steam space above the water level 60 then flows through the tube 'into the chamber 17 and then downwardly through the tubes l6 connected to the chamber 17 into the chamber 19. After passing through the chamber 19, the steam flows upwardly through the tubes 16 into the chamber 18 and leaves the boiler in the form of superheated steam through the tube 21.

Referring to Fig. 4, the flue gas duct 2' can also be constructed with a square cross-section and can be arranged in the water space so that one of the two diagonals of the cross-section is vertical. In this construction, the flue gas duct 2' contains tubes 5' over which the flue gas flows transversely and which are open to the water space and are arranged in groups in mutually parallel planes perpendicular to the direction of flue gas flow. In contrast to the construction shown in FIGS. 1 to 3, however, the tubes 5 are arranged in successive planes in criss-cross relation. In addition, the

ends of the tubes 5 are welded in fluid-tight fashion into the walls of the flue gas duct 2', which are at rightangles to the tubes 5' so that the walls are effectively reinforced and prevented from buckling. Here, there are no wall tubes corresponding to the finned tubes 9. It may, however, be convenient to provide such wall tubes at least in that portion of the flue gas duct which is under the highest'stress from the hot flue gas. In the construction'shown, the tubes 5 have separate extencessible than if the extensions are integral with the tubes.

. Referring to FIG. 5, the flue gas duct 2" can also be constructed with a rhomboid cross-section with the tubes 5" arranged as in FIG. 4. Because the cross-section is rhomboid, the tubes '5" are v at a somewhat steeper angle than as shown in FIG. 4, so that the steam bubbles can flow down out of the tubes somewhat better.

In the constructions of FIGS. 4 and 5, that portion of the flue gas duct having tubes 5 or 5" open to the water space can be followed by tubes corresponding to the steam-carrying tubes 16 in FIG. 1. If so, these tubes are preferably arranged in the same way as the tubes 5' and 5".

What is claimed is:

l. A steam boiler having a water space, a flue gas duct traversing said water space, a muffle burner at the mouth of said flue gas duct for directing a flow of flue gas into said duct, and a plurality of tubes open to said water space and mounted in said flue duct at least in a 'portion of said duct directlyadjacent said. muffle.

5. A steam boiler as set forth in claim 4 wherein each vertical wall includes a row of mutually adjacent finned tubes secured together in seal-tight manner, said finned tubes being open to said water space.

6. A steam boiler as set forth in claim 3 wherein said duct is of a square cross-section with a diagonal disposed in a vertical plane.

7. A steam boiler as set forth in claim 6 wherein said tubes are arranged in groups in mutually parallel planes parallel to two mutually opposite walls of said duct, said groups being disposed in an alternating criss-cross pattern.

8. A steam boiler as set forth in claim 3 wherein said duct is of a rhomboid cross-section with a diagon disposed in a vertical plane.

9. A steam boiler as set forth in claim 8 wherein said tubes are arranged in groups in mutually parallel planes parallel to two mutually opposite walls of said duct, said groups being disposed in an alternating criss-cross pattern.

10. A steam boiler as set forth in claim 1 wherein at least some of said tubes project upwardly beyond said duct.

11. A steam boiler as set forth in claim 1 wherein at least some of said tubes include extension tubes projecting upwardly beyond said duct and angularly disposed with respect to the remainder of said tubes in said duct.

12. A steam boiler as set forth in claim 1 which further has a plurality of tubes located in a second portion of said flue duct downstream of the flow of flue gas in transverse relation to the flue gas flow, said latter tubes being in communication with a space above said water space to conduct a flow of steam from above said water space therethrough.

13. A steam boiler as set forth in claim 12 which further comprises a plurality of tubes open to said water space and located in a remaining portion of said flue duct downstream of said latter tubes in the flow of flue gas in transverse relation to the flue gas flow.

14. A steam boiler as set forth in claim 1 which further includes means for feeding feed water into said water space.

15. A steam boiler as set forth in claim 14 wherein said means includes a plurality of nozzles for forcing feed water fed into said water space into the foremost of said tubes adjacent said muffle burner.

16. A steam boiler having a water space, a flue gas duct traversing said water space in water tight relation thereto, a muffle burner coaxially mounted at the mouth of said flue gas duct for directing a flow of flue gas axiallyv into said duct, and a plurality of tubes mounted in said flue duct at least in a portion of said duct adjacent said muffle burner and transverse to the flow of flue gas therein, said tubes being open at opposite ends thereof to said water space to conduct water therethrough in heat exchange relation to the flue gas in said flue gas duct.

17. A steam boiler having a water space; a flue gas duct traversing said water space, said duct including two horizontal walls and two vertical walls with said tubes connected to said horizontal walls, each said vertical wall including a row of mutually adjacent finned tubes secured together in seal-tight manner, said finned tubes being open to said water space; a muffle burner at the mouth of said flue gas duct for directing a flow of flue gas into said duct; and a plurality of tubes open to said water space and mounted in said flue duct at least in a portion of said duct adjacent said muffle burner and transverse to the flow of flue gas therein. 

1. A steam boiler having a water space, a flue gas duct traversing said water space, a muffle burner at the mouth of said flue gas duct for directing a flow of flue gas into said duct, and a plurality of tubes open to said water space and mounted in said flue duct at least in a portion of said duct directly adjacent said muffle burner and transverse to the flow of flue gas therein.
 2. A steam boiler as set forth in claim 1 wherein said tubes are arranged in groups in mutually parallel planes perpendicular to the direction of flow of flue gas.
 3. A steam boiler as set forth in claim 1 wherein said duct is of a quadrilateral cross-section.
 4. A steam boiler as set forth in claim 3 wherein said duct includes two horizontal walls and two vertical walls with said tubes connected to said horizontal walls.
 5. A steam boiler as set forth in claim 4 wherein each vertical wall includes a row of mutually adjacent finned tubes secured together in seal-tight manner, said finned tubes being open to said water space.
 6. A steam boiler as set forth in claim 3 wherein said duct is of a square cross-section with a diagonal disposed in a vertical plane.
 7. A steam boiler as set forth in claim 6 wherein said tubes are arranged in groups in mutually parallel planes parallel to two mutually opposite walls of said duct, said groups being disposed in an alternating criss-cross pattern.
 8. A steam boiler as set forth in claim 3 wherein said duct is of a rhomboid cross-section with a diagonal disposed in a vertical plane.
 9. A steam boiler as set forth in claim 8 wherein said tubes are arranged in groups in mutually parallel planes parallel to two mutually opposite walls of said duct, said groups being disposed in an alternating criss-cross pattern.
 10. A steam boiler as set forth in claim 1 wherein at least some of said tubes project upwardly beyond said duct.
 11. A steam boiler as set forth in claim 1 wherein at least some of said tubes include extension tubes projecting upwardly beyond said duct and angularly disposed with respect to the remainder of said tubes in said duct.
 12. A steam boiler as set forth in claim 1 which further has a plurality of tubes located in a second portion of said flue duct downstream of the flow of flue gas in transverse relation to the flue gas flow, said latter tubes being in communication with a space above said water space to conduct a flow of steam from above said water space therethrough.
 13. A steam boiler as set forth in claim 12 which further comprises a plurality of tubes open to said water space and located in a remaining portion of said flue duct downstream of said latter tubes in the flow of flue gas in transverse relation to the flue gas flow.
 14. A steam boiler as set forth in claim 1 which further includes means for feeding feed water into said water space.
 15. A steam boiler as set forth in claim 14 wherein said means includes a plurality of nozzles for forcing feed water fed into said water space into the foremost of said tubes adjacent said muffle burner.
 16. A steam boiler having a water space, a flue gas duct traversing said water space in water tight relation thereto, a muffle burner coaxially mounted at the mouth of said flue gas duct for directing a flow of flue gas axially into said duct, and a plurality of tubes mounted in said flue duct at least in a portion of said duct adjacent said muffle burner and transverse to the flow of flue gas therein, said tubes being open at opposite ends thereof to said water space to conduct water therethrough in heat exchange relation to the flue gas In said flue gas duct.
 17. A steam boiler having a water space; a flue gas duct traversing said water space, said duct including two horizontal walls and two vertical walls with said tubes connected to said horizontal walls, each said vertical wall including a row of mutually adjacent finned tubes secured together in seal-tight manner, said finned tubes being open to said water space; a muffle burner at the mouth of said flue gas duct for directing a flow of flue gas into said duct; and a plurality of tubes open to said water space and mounted in said flue duct at least in a portion of said duct adjacent said muffle burner and transverse to the flow of flue gas therein. 